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Posted: October 2014

Genetically Modified (GM) Insect-Resistant Rice and Weedy Rice Hybrids Have Increased Seed Production

There is a major concern that if genetically modified crops pollinate closely related weeds, the crop/weed hybrids will survive and spread in the larger environment. Researchers in China have found that insect-resistant rice and weedy rice hybrids, under conditions of normal pest pressure, show (as intended) less insect damage, but, unexpectedly, produce more seeds than both nontransgenic rice and weedy rice controls (Wang et al. 2011).

Weedy rice is one of the main weeds in and around rice fields. It actually belongs to the same species as cultivated rice. Although both cultivated rice and weedy rice normally self-pollinate, they do also cross-pollinate with one another under field conditions and produce fertile and persisting hybrid offspring. If GM insect-resistant cultivated rice were to pollinate weedy rice, the offspring could also be insect-resistant and create populations of insect-resistant cultivated rice/weedy rice hybrids that could spread in and among fields.

Wang et al. took a variety of GM insect-resistant rice that contains two different types of insect-resistance genes (Bt and cowpea trypsin inhibitor) and crossed it with weedy rice. They examined the offspring of second and third hybrid generations under low and natural insect pressure conditions. They found that under natural insect pressure the offspring of third generation hybrids “had 79% less insect damage” and, surprisingly, “produced 47% more seeds than their nontransgenic counterparts” and also “44% more seeds than their weedy parents.” This significant increase in seed production by the individual hybrid plants was unexpected.

Even small numbers of such insect-resistant crop/weed hybrids occurring in field conditions could have significant impact, since the hybrids could then reproduce through self-pollination and quickly generate many seeds and transgenic offspring. The authors state that these “transgenes could increase in frequency in weedy rice populations when target insects are sufficiently common, perhaps contributing to larger seed banks and more pervasive weedy rice problems, at least in the short term.”

Wang, X., Xia, H., Wang, W. et al. (2011). “Transgenes for Insect Resistance Reduce Herbivory and Enhance Fecundity in Advanced Generations of Crop-Weed Hybrids of Rice,” Evolutionary Applications vol. 4, pp. 672-84. doi: 10.1111/j.1752-4571.2011.00190.x (available free online:

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